I love early morning walks.. Right at the sunrise is the best, with colors of the sky changing in front of your eyes..
Plus, on the practical side, to go early is the only way I can take my boy Ari out for an hour or so before leaving for work.
The problem is that he is not a morning dog, and prefers to sleep late.

Question - is there any harm in waking up a sleeping dog, and sort of pushing him a bit to get going?

I see nothing wrong with getting him up and out early even though he might rather sleep. I would think it's all in how you get him up and motivate him. Calling to him, rattling a treat jar, jingling his harness and leash, etc. rather than going over and giving your sleeping dog a little shake (a big no no, but I am sure you already know that).

The thing with dogs is that they aren't on the same daily schedule as we are. Once we're up, we know it's going to be a long time till we're back under the sheets again. Your dog can hit his sleep mat the second you guys get home from your walk. And since you say he loves the walks once up and about then I say go for it and enjoy that early morning time with your dog (it's my favorite time too, actually).

Rupert's the same. I have to get him up and make him go out in the morning, he'd much rather just sleep in. And oh man did he used to kick up a fuss at being woken up at 5am to go for a walk before I left for work. Now that I'm not working our first "walk" of the day is literally just outside to the bush and back again though, neither of us really do mornings

Annie can be in a very deep sleep, dreaming, snoring, and the works... but the second she hears me get her leash and harness out--- no matter how quiet I am about it, she's awake and dancing in front of me before I can blink. Maybe it will work for your big boy, especially if you aren't trying to be all that quiet.

If an opportunity comes to you in life, say yes first, even if you don't know how to do it.

When my boy hears me getting up, making noise, leash, harness, cookie jar - he just curls up in his bed, trying to become invisible, and pretends that he is in deep sleep. And if I come over and stand over him, he looks up at me with those wise ridgeback eyes, full of eternal sadness and pity for mankind, as if saying "I am so tired... So tired... You never let me sleep..."

He could win a Dog Oscar for the best role of a Very Tired Dog, or a Very Hungry Dog, if there were such thing

When my boy hears me getting up, making noise, leash, harness, cookie jar - he just curls up in his bed, trying to become invisible, and pretends that he is in deep sleep. And if I come over and stand over him, he looks up at me with those wise ridgeback eyes, full of eternal sadness and pity for mankind, as if saying "I am so tired... So tired... You never let me sleep..."

He could win a Dog Oscar for the best role of a Very Tired Dog, or a Very Hungry Dog, if there were such thing

Rupert does exactly the same when it's raining. I insisted on him going out in the pouring rain the other day, it had been about 6 hours since he'd been out so I figured he must need a pee. Well he stood there on the grass, staring at me over his muzzle, head hanging so low it almost touched the grass, tail between the back legs, back all hunched up against the oh so evil rain and his ears sticking out to the side. He could have been the poster dog for a campaign against cruelty to animals Once he realised that yes, I really did mean to make him potty in THAT he had the worlds quickest pee and practically dragged me back to the front door which he then kept pushing with his nose while I struggled to unlock it. Apparently Rupert Bears melt if out in the rain too long.

We have one of each type of dog.
The pup is set to wake us up at 7am without fail (thats when boyfriend gets up for work)
My dog will sleep til noon if you let him, but mostly is happy to get up when I get up to go for his walk.
Dog 3 will not budge, even if I wake her up and treat her and put the lead on her 9 times out of 10 she just won't shift off the sofa, or will get as far as the door and pull to go back inside. I usually make a token effort to invite her for a walk and then leave her behind and walk her later. No amount of bribery or bullying will budge her.

The pups so cute when she's asleep and wakes up when she's still so tired she can hardly walk. Like if she's asleep in her basket and I move into the other room she'll drag herself out of bed and into the room I'm in and then just flop, its the funniest/cutest thing ever.